Advances in chemical protein modification

Diseleno-albumin, a native bio-inspired drug free therapeutic protein induces apoptosis in lung cancer cells through mitochondrial oxidation

Macromolecular therapeutic is the emerging concept in the fields of drug delivery and drug discovery. The present study reports the design and development of a serum albumin based macromolecular chemotherapeutic by conjugating bovine serum albumin (BSA) with 3,3'-diselenodipropionic acid (DSePA), a pharmacologically active organo-diselenide (R-Se-Se-R). The reaction conditions were optimised to achieve the controlled conjugation of BSA with DSePA without causing any significant alteration in its physico-chemical properties or secondary structure and crosslinking. The chemical characterisation of the reaction product through various spectroscopic techniques viz., FT-IR, Raman, XPS, AAS and MALDI-TOF-MS, established the conjugation of about ∼5 DSePA molecules per BSA molecule. The DSePA conjugated BSA (Se-Se-BSA) showed considerable stability in aqueous and lyophilized forms. The cytotoxicity studies by involving cell lines of cancerous and non-cancerous origins indicated that Se-Se-BSA selectively inhibited the proliferation of cancerous cells. The cellular uptake studies by physically labelling Se-Se-BSA with curcumin and following its intracellular fluorescence confirmed that uptake efficiency of Se-Se-BSA was almost similar to that of native BSA. Finally, studies on the mechanism of action of Se-Se-BSA in the A549 (lung adenocarcinoma) cells revealed that it induced mitochondrial ROS generation followed by mitochondrial dysfunction, activation of caspases and apoptosis. Together, these results demonstrate a bio-inspired approach of exploring diselenide (-Se-Se-) grafted serum albumin as the potential drug free therapeutic for anticancer application.

Luminescent lanthanide metallopeptides for biomolecule sensing and cellular imaging

Lanthanide ions display unique luminescent properties that make them particularly attractive for the development of bioprobes, including long-lived excited states that allow the implementation of time-gated experiments and the elimination of background fluorescence associated with biological media, as well as narrow emission bands in comparison with typical organic fluorophores, which allow ratiometric and multiplex assays. These luminescent complexes can be combined with peptide ligands to endow them with additional targeting, responsiveness, and selectivity, thus multiplying the opportunities for creative probe design. In this feature article we will present some of the main strategies that researchers have used to develop lanthanide metallopeptide probes for the detection of proteins and nucleic acids, as well as for monitoring enzymatic activity and cellular imaging.

Controlling (E/Z)-Stereoselectivity of -NHC=O Chlorination: Mechanism Principles for Wide Scope Applications

Organic halogen compounds are cornerstones of applied chemical sciences. Halogen substitution is a smart molecular design strategy adopted to influence reactivity, membrane permeability and receptor interaction. Chiral bioreceptors may restrict the stereochemical requirements in the halo-ligand design. Straightforward (but expensive) catalyzed stereospecific halogenation has been reported. Historically, PCl5 served access to uncatalyzed stereoselective chlorination although the stereochemical outcomes were influenced by steric parameters. Nonetheless, stereochemical investigation of PCl5 reaction mechanism with carbamoyl (RCONHX) compounds has never been addressed. Herein, we provide the first comprehensive stereochemical mechanistic explanation outlining halogenation of carbamoyl compounds with PCl5; the key regioselectivity-limiting nitrilimine intermediate (8-Z.HCl); how substitution pattern influences regioselectivity; why oxadiazole byproduct (P1) is encountered; stereo-electronic factors influencing the hydrazonoyl chloride (P2) production; and discovery of two stereoselectivity-limiting parallel mechanisms (stepwise and concerted) of elimination of HCl and POCl3. DFT calculations, synthetic methodology optimization, X-ray evidence and experimental reaction kinetics study evidence all supported the suggested mechanism proposal (Scheme 2). Finally, we provide mechanism-inspired future recommendations for directing the reaction stereoselectivity toward elusive and stereochemically inaccessible (E)-bis-hydrazonoyl chlorides along with potentially pivotal applications of both (E/Z)-stereoisomers especially in medicinal chemistry and protein modification.

Fast and Selective Cysteine Conjugation Using para-Quinone Methides

An efficient and selective method for cysteine conjugation utilizing para-quinone methides (p-QMs) was developed. p-QM labeling exhibits high specificity toward the cysteine residue, as evidenced by its reactivity with various amino acid derivatives, peptides, and proteins. Notably, the p-QM-cysteine reactions display robust kinetics with rate constants up to 1.67 × 104 M-1·s-1. Furthermore, p-QM conjugation enables us to attach a fluorescent probe to a HER2 nanobody, resulting in selective labeling of HER2-positive SK-BR-3 cells.

Molecular recognition of peptides and proteins by cucurbit[n]urils: systems and applications

The development of methodology for attaching ligand binding sites to proteins of interest has accelerated biomedical science. Such protein tags have widespread applications as well as properties that significantly limit their utility. This review describes the mechanisms and applications of supramolecular systems comprising the synthetic receptors cucurbit[7]uril (Q7) or cucurbit[8]uril (Q8) and their polypeptide ligands. Molecular recognition of peptides and proteins occurs at sites of 1-3 amino acids with high selectivity and affinity via several distinct mechanisms, which are supported by extensive thermodynamic and structural studies in aqueous media. The commercial availability, low cost, high stability, and biocompatibility of these synthetic receptors has led to the development of myriad applications. This comprehensive review compiles the molecular recognition studies and the resulting applications with the goals of providing a valuable resource to the community and inspiring the next generation of innovation.

Protocol for protein modification using oxalyl thioester-mediated chemoselective ligation

The development of fast ligation chemistries for the site-specific modification of proteins has become a major focus in chemical biology. We describe steps for preparing an oxalyl thioester precursor in the form of an N-oxalyl perhydro-1,2,5-dithiazepine handle, i.e., the oxoSEA group, and incorporating it into a peptide modifier using solid phase peptide synthesis. We then detail procedures for its application for the modification of an N-terminal Cys-containing B1 domain of the streptococcal G protein using the native chemical ligation. For complete details on the use and execution of this protocol, please refer to Snella et al.1.

Computer-Aided Site-Specific PEGylation of PET Hydrolases for Enhanced PET Degradation

The enormous accumulation of poly(ethylene terephthalate) (PET) waste has posed a serious threat to the environment and human health, and biodegradation with PET hydrolase (PETase) can be a possible solution. Herein, we propose site-specifically modifying PETase with amphiphilic polymers to improve the enzyme performance at ambient temperature. For this purpose, we devise a computer-aided strategy to prioritize the conjugation site, and polyethylene glycol (PEG) preparations of 0.55 to 10 kDa are site-specifically conjugated to PETase. The most active conjugate PETase-PEG 5k (PETase-5K) shows an increase of melting temperature (3.88 °C) and significantly improves PET degradation performance (3.5- and 3.1-fold increases at 30 and 40 °C, respectively). Experimental investigation and molecular dynamics simulations reveal that the site-specific PEGylation increases the hydrophobic solvent-accessible surface area and the binding capability to the PET surface, thickens the hydration layer, increases the intramolecular hydrogen bonding, reduces the interactions between water and the conjugated enzyme surface, and rigidifies the enzyme structure via hydrogen bonding and hydrophobic interactions between the polymer and the enzyme, thus leading to improved enzymatic performance of PETase-5K. We further validate the versatility of the site-specific PEGylation in one of the most evolved variants of PETase, FAST-PETase, by 1.8-fold improvement in PET degradation at 30 °C. The presented computer-aided site-specific conjugation strategy has opened a new avenue to enhancing PETase performance at ambient temperature, and the contribution of PEGylation to PETase unraveled in this work laid a foundation for the rational engineering of PET hydrolases.

Synthesis of non-canonical amino acids through dehydrogenative tailoring

Amino acids are essential building blocks in biology and chemistry. Whereas nature relies on a small number of amino acid structures, chemists desire access to a vast range of structurally diverse analogues1-3. The selective modification of amino acid side-chain residues represents an efficient strategy to access non-canonical derivatives of value in chemistry and biology. While semisynthetic methods leveraging the functional groups found in polar and aromatic amino acids have been extensively explored, highly selective and general approaches to transform unactivated C-H bonds in aliphatic amino acids remain less developed4,5. Here we disclose a stepwise dehydrogenative method to convert aliphatic amino acids into structurally diverse analogues. The key to the success of this approach lies in the development of a selective catalytic acceptorless dehydrogenation method driven by photochemical irradiation, which provides access to terminal alkene intermediates for downstream functionalization. Overall, this strategy enables the rapid synthesis of new amino acid building blocks and suggests possibilities for the late-stage modification of more complex oligopeptides.

Late-Stage Halogenation of Complex Substrates with Readily Available Halogenating Reagents

ConspectusLate-stage halogenation, targeting specific positions in complex substrates, has gained significant attention due to its potential for diversifying and functionalizing complex molecules such as natural products and pharmaceutical intermediates. Utilizing readily available halogenating reagents, such as hydrogen halides (HX), N-halosuccinimides (NXS), and dichloroethane (DCE) reagents for late-stage halogenation shows great promise for expanding the toolbox of synthetic chemists. However, the reactivity of haleniums (X+, X = Cl, Br, I) can be significantly hindered by the presence of various functional groups such as hydroxyl, amine, amide, or carboxylic acid groups. The developed methods of late-stage halogenation often rely on specialized activating reagents and conditions. Recently, our group (among others) has put great efforts into addressing these challenges and unlocking the potential of these readily available HX, NXS, and DCE reagents in complex molecule halogenation. Developing new methodologies, catalyst systems, and reaction conditions further enhanced their utility, enabling the efficient and selective halogenation of intricate substrates.With the long-term goal of achieving selective halogenation of complex molecules, we summarize herein three complementary research topics in our group: (1) Efficient oxidative halogenations: Taking inspiration from naturally occurring enzyme-catalyzed oxidative halogenation reactions, we focused on developing cost-effective oxidative halogenation reactions. We found the combination of dimethyl sulfoxide (DMSO) and HX (X = Cl, Br, I) efficient for the oxidative halogenation of aromatic compounds and alkenes. Additionally, we developed electrochemical oxidative halogenation using DCE as a practical chlorinating reagent for chlorination of (hetero)arenes. (2) Halenium reagent activation: Direct electrophilic halogenation using halenium reagents is a reliable method for obtaining organohalides. However, compared to highly reactive reagents, the common and readily available NXS and dihalodimethylhydantoin (DXDMH) demonstrate relatively lower reactivity. Therefore, we focused on developing oxygen-centered Lewis base catalysts such as DMSO, 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and nitromethane to activate NXS or DXDMH, enabling selective halogenation of bioactive substrates. (3) Halogenation of inert substrates: Some substrates, such as electron-poor arenes and pyridines, are inert toward electrophilic functionalization reactions. We devised several strategies to enhance the reactivity of these molecules. These strategies, characterized by mild reaction conditions, the ready availability and stability of catalysts and reagents, and excellent tolerance for various functional groups, have emerged as versatile protocols for the late-stage aromatic halogenation of drugs, natural products, and peptides. By harnessing the versatility and selectivity of these catalysts and methodologies, synthetic chemists can unlock new possibilities in the synthesis of halogenated compounds, paving the way for the development of novel functional materials and biologically active molecules.

Inhibition of SARS-CoV-2 3CLpro by chemically modified tyrosinase from Agaricus bisporus

Antiviral compounds are crucial to controlling the SARS-CoV-2 pandemic. Approved drugs have been tested for their efficacy against COVID-19, and new pharmaceuticals are being developed as a complementary tool to vaccines. In this work, a cheap and fast purification method for natural tyrosinase from Agaricus bisporus (AbTyr) fresh mushrooms was developed to evaluate the potential of this enzyme as a therapeutic protein via the inhibition of SARS-CoV-2 3CLpro protease activity in vitro. AbTyr showed a mild inhibition of 3CLpro. Thus, different variants of this protein were synthesized through chemical modifications, covalently binding different tailor-made glycans and peptides to the amino terminal groups of the protein. These new tyrosinase conjugates were purified and characterized through circular dichroism and fluorescence spectroscopy analyses, and their stability was evaluated under different conditions. Subsequently, all these tyrosinase conjugates were tested for 3CLpro protease inhibition. From them, the conjugate between tyrosinase and a dextran-aspartic acid (6 kDa) polymer showed the highest inhibition, with an IC50 of 2.5 μg ml-1 and IC90 of 5 μg ml-1, with no cytotoxicity activity by polymer insertion. Finally, SARS-CoV-2 virus infection was studied. It was found that this new AbTyr-Dext6000 protein showed an 80% decrease in viral load. These results show the capacity of these tyrosinase bioconjugates as potential therapeutic proteins, opening the possibility of extension and applicability against other different viruses.

Cobalt-catalyzed hydrothiolation of alkynes for the diverse synthesis of branched alkenyl sulfides

Alkenyl sulfides have gained increasing prominence in medicinal chemistry and materials. Hydrothiolation of alkynes for the diverse synthesis of alkenyl sulfides is an appealing method. Herein, we report a cobalt-catalyzed Markovnikov hydromethylthiolation of alkynes to afford branched alkenyl methylsulfanes with good yields and high regioselectivity. This method also enables the diverse synthesis of branched alkenyl sulfides. The reaction shows good functional group tolerance and could be scaled up. The mechanistic studies including control experiments, deuterium-labeling experiments, and Hammett plot indicated alkynes insertion followed by electrophilic thiolation pathway.

Cysteinylprolyl ester-mediated drug release from a lipid-drug conjugate

For small-molecule drugs, lipidation via a cleavable linkage can extend half-life in circulation through interaction with albumin. Here we modified the cysteinylprolyl ester (CPE) system used in peptide thioester synthesis, which normally requires basic conditions, for use as an self-immolative linker and release device for a lipid-gemcitabine conjugate. To improve release under physiological conditions for medical application, a methyl group at the α-position of cysteine on the CPE unit was incorporated in anticipation of the Thorpe-Ingold effect. As a result, Ac-Gly-(α-Me)Cys(SH)-Pro-gemcitabine 11 drastically promoted the release of gemcitabine in comparison with Ac-Gly-Cys(SH)-Pro-gemcitabine 10. Furthermore, in the presence of bovine serum albumin and/or 2-mercaptoethanesulfonic acid, the gentle and continuous release of gemcitabine from the lipid-gemcitabine conjugate 16 was achieved. In addition to gemcitabine, this method could allow high clearance drugs, including nucleic acid and prostacyclin derivatives, to maintain their biological activity long enough to become effective.

Repurposing a plant peptide cyclase for targeted lysine acylation

Transpeptidases are powerful tools for protein engineering but are largely restricted to acting at protein backbone termini. Alternative enzymatic approaches for internal protein labelling require bulky recognition motifs or non-proteinogenic reaction partners, potentially restricting which proteins can be modified or the types of modification that can be installed. Here we report a strategy for labelling lysine side chain ε-amines by repurposing an engineered asparaginyl ligase, which naturally catalyses peptide head-to-tail cyclization, for versatile isopeptide ligations that are compatible with peptidic substrates. We find that internal lysines with an adjacent leucine residue mimic the conventional N-terminal glycine-leucine substrate. This dipeptide motif enables efficient intra- or intermolecular ligation through internal lysine side chains, minimally leaving an asparagine C-terminally linked to the lysine side chain via an isopeptide bond. The versatility of this approach is demonstrated by the chemoenzymatic synthesis of peptides with non-native C terminus-to-side chain topology and the conjugation of chemically modified peptides to recombinant proteins.

Evolution of Pyrrolysyl-tRNA Synthetase: From Methanogenesis to Genetic Code Expansion

Over 20 years ago, the pyrrolysine encoding translation system was discovered in specific archaea. Our Review provides an overview of how the once obscure pyrrolysyl-tRNA synthetase (PylRS) tRNA pair, originally responsible for accurately translating enzymes crucial in methanogenic metabolic pathways, laid the foundation for the burgeoning field of genetic code expansion. Our primary focus is the discussion of how to successfully engineer the PylRS to recognize new substrates and exhibit higher in vivo activity. We have compiled a comprehensive list of ncAAs incorporable with the PylRS system. Additionally, we also summarize recent successful applications of the PylRS system in creating innovative therapeutic solutions, such as new antibody-drug conjugates, advancements in vaccine modalities, and the potential production of new antimicrobials.

Integrating Computational Design and Experimental Approaches for Next-Generation Biologics

Therapeutic protein engineering has revolutionized medicine by enabling the development of highly specific and potent treatments for a wide range of diseases. This review examines recent advances in computational and experimental approaches for engineering improved protein therapeutics. Key areas of focus include antibody engineering, enzyme replacement therapies, and cytokine-based drugs. Computational methods like structure-based design, machine learning integration, and protein language models have dramatically enhanced our ability to predict protein properties and guide engineering efforts. Experimental techniques such as directed evolution and rational design approaches continue to evolve, with high-throughput methods accelerating the discovery process. Applications of these methods have led to breakthroughs in affinity maturation, bispecific antibodies, enzyme stability enhancement, and the development of conditionally active cytokines. Emerging approaches like intracellular protein delivery, stimulus-responsive proteins, and de novo designed therapeutic proteins offer exciting new possibilities. However, challenges remain in predicting in vivo behavior, scalable manufacturing, immunogenicity mitigation, and targeted delivery. Addressing these challenges will require continued integration of computational and experimental methods, as well as a deeper understanding of protein behavior in complex physiological environments. As the field advances, we can anticipate increasingly sophisticated and effective protein therapeutics for treating human diseases.

Discovery and development of tyrosine-click (Y-click) reaction for the site-selective labelling of proteins

With the versatile utility of bio-conjugated peptides and proteins in the fields of agriculture, food, cosmetics and pharmaceutical industry, the design of smart protocols to conjugate and modulate biomolecules becomes highly desirable. During this process, the most important consideration for biochemists is the retention of configurational integrity of the biomolecules. Moreover, this type of bioconjugation of peptide and protein becomes frivolous if the reaction is not performed with precise amino acid residues. Hence, chemo-selective, as well as site-selective reactions, that are biocompatible and possess an appropriate level of reactivity are necessary. Based on click chemistry, there are so many tyrosine (Y) conjugation strategies, such as sulfur-fluoride exchange (SuFEx), sulfur-triazole exchange (SuTEx), coupling with π-allyl palladium complexes, diazonium salts, diazodicarboxyamide-based reagents etc. Among these techniques, diazodicarboxyamide-based Y-conjugation, which is commonly known as the "tyrosine-click (Y-click) reaction", has met the expectations of synthetic and biochemists for the tyrosine-specific functionalization of biomolecules. Over the past one and a half decades, significant progress has been made in the classical organic synthesis approach, as well as its biochemical, photochemical, and electrochemical variants. Despite such progress and increasing importance, the Y-click reaction has not been reviewed to document variations in its methodology, applications, and broad utility. The present article aims to provide a summary of the approaches for the modulation of biomolecules at the hotspot of tyrosine residue by employing the Y-click reaction. The article also highlights its application for the mapping of proteins, imaging of living cells, and in the fields of analytical and medicinal chemistry.

Improving the stability of insulin through effective chemical modifications: A Comprehensive review

Insulin, an essential peptide hormone, conjointly regulates blood glucose levels by its receptor and it is used as vital drug to treat diabetes. This therapeutic hormone may undergo different chemical modifications during industrial processes, pharmaceutical formulation, and through its endogenous storage in the pancreatic β-cells. Insulin is highly sensitive to environmental stresses and readily undergoes structural changes, being also able to unfold and aggregate in physiological conditions. Even; small changes altering the structural integrity of insulin may have significant impacts on its biological efficacy to its physiological and pharmacological activities. Insulin analogs have been engineered to achieve modified properties, such as improved stability, solubility, and pharmacokinetics, while preserving the molecular pharmacology of insulin. The casually or purposively strategies of chemical modifications of insulin occurred to improve its therapeutic and pharmaceutical properties. Knowing the effects of chemical modification, formation of aggregates, and nanoparticles on protein can be a new look at the production of protein analogues drugs and its application in living system. The project focused on effects of chemical modifications and nanoparticles on the structure, stability, aggregation and their results in effective drug delivery system, biological activity, and pharmacological properties of insulin. The future challenge in biotechnology and pharmacokinetic arises from the complexity of biopharmaceuticals, which are often molecular structures that require formulation and delivery strategies to ensure their efficacy and safety.

Kinetic Resolution of Epimeric Proteins Enables Stereoselective Chemical Mutagenesis

Chemical mutagenesis via dehydroalanine (Dha) is a powerful method to tailor protein structure and function, allowing the site-specific installation of post-translational modifications and non-natural functional groups. Despite the impressive versatility of this method, applications have been limited, as products are formed as epimeric mixtures, whereby the modified amino acid is present as both the desired l-configuration and a roughly equal amount of the undesired d-isomer. Here, we describe a simple remedy for this issue: removal of the d-isomer via proteolysis using a d-stereoselective peptidase, alkaline d-peptidase (AD-P). We demonstrate that AD-P can selectively cleave the d-isomer of epimeric residues within histone H3, GFP, Ddx4, and SGTA, allowing the installation of non-natural amino acids with stereochemical control. Given the breadth of modifications that can be introduced via Dha and the simplicity of our method, we believe that stereoselective chemoenzymatic mutagenesis will find broad utility in protein engineering and chemical biology applications.

Orthogonal bioconjugation targeting cysteine-containing peptides and proteins using alkyl thianthrenium salts

Late-stage specific and selective diversifications of peptides and proteins performed at target residues under ambient conditions are recognized to be the most facile route to various and abundant conjugates. Herein, we report an orthogonal modification of cysteine residues using alkyl thianthreium salts, which proceeds with excellent chemoselectivity and compatibility under mild conditions, introducing a diverse array of functional structures. Crucially, multifaceted bioconjugation is achieved through clickable handles to incorporate structurally diverse functional molecules. This "two steps, one pot" bioconjugation method is successfully applied to label bovine serum albumin. Therefore, our technique is a versatile and powerful tool for late-stage orthogonal bioconjugation.

Hypervalent Iodine Amino Acid Building Blocks for Bioorthogonal Peptide Macrocyclization

Ethynylbenziodoxol(on)es (EB(X)xs) reagents have emerged as useful reagents for peptide/protein modification due to their versatile reactivity and high selectivity. Herein, we report the successful introduction of ethynylbenziodoxoles (EBxs) on different amino acid building blocks (Lys/Orn/Dap), and show their compatibility with both solid phase peptide synthesis (SPPS) and solution phase peptide synthesis (SPS). The selective incorporation of the EBx core into peptide sequences enable efficient macrocyclizations under mild conditions for the synthesis of topologically unique cyclic and bicyclic peptides.

Nanoparticle-Based Drug Delivery Systems in Inhaled Therapy: Improving Respiratory Medicine

Inhaled nanoparticle (NP) therapy poses intricate challenges in clinical and pharmacodynamic realms. Recent strides have revolutionized NP technology by enabling the incorporation of diverse molecules, thus circumventing systemic clearance mechanisms and enhancing drug effectiveness while mitigating systemic side effects. Despite the established success of systemic NP delivery in oncology and other disciplines, the exploration of inhaled NP therapies remains relatively nascent. NPs loaded with bronchodilators or anti-inflammatory agents exhibit promising potential for precise distribution throughout the bronchial tree, offering targeted treatment for respiratory diseases. This article conducts a comprehensive review of NP applications in respiratory medicine, highlighting their merits, ranging from heightened stability to exacting lung-specific delivery. It also explores cutting-edge technologies optimizing NP-loaded aerosol systems, complemented by insights gleaned from clinical trials. Furthermore, the review examines the current challenges and future prospects in NP-based therapies. By synthesizing current data and perspectives, the article underscores the transformative promise of NP-mediated drug delivery in addressing chronic conditions such as chronic obstructive pulmonary disease, a pressing global health concern ranked third in mortality rates. This overview illuminates the evolving landscape of NP inhalation therapies, presenting optimistic avenues for advancing respiratory medicine and improving patient outcomes.

Ex Situ Gaseous Reagent for Multicomponent Amine Bioconjugation

We report a minimalist gaseous sulfonyl-chloride-derived reagent for multicomponent bioconjugation with amine, phenol, or aniline reagents to afford urea or carbamate products. With the utilization of a gas-phase reagent for a reaction mediated by metal ions, a variety of biologically relevant molecules, such as saccharide, poly(ethylene glycol), fluorophore, and affinity tag, can be efficiently cross-linked to the N terminus or lysine side-chain amines on natural polypeptides or proteins.

Antibody Drug Conjugates for Cancer Therapy: From Metallodrugs to Nature-Inspired Payloads

This review highlights significant advancements in antibody-drug conjugates (ADCs) equipped with metal-based and nature-inspired payloads, focusing on synthetic strategies for antibody conjugation. Traditional methods such us maleimide and succinimide conjugation and classical condensation reactions are prevalent for metallodrugs and natural compounds. However, emerging non-conventional strategies such as photoconjugation are gaining traction due to their milder conditions and, in an aspect which minimizes side reactions, selective formation of ADC. The review also summarizes the therapeutic and diagnostic properties of these ADCs, highlighting their enhanced selectivity and reduced side effects in cancer treatment compared to non-conjugated payloads. ADCs combine the specificity of monoclonal antibodies with the cytotoxicity of chemotherapy drugs, offering a targeted approach to the elimination of cancer cells while sparing healthy tissues. This targeted mechanism has demonstrated impressive clinical efficacy in various malignancies. Key future advancements include improved linker technology for enhanced stability and controlled release of cytotoxic agents, incorporation of novel, more potent, cytotoxic agents, and the identification of new cancer-specific antigens through genomic and proteomic technologies. ADCs are also expected to play a crucial role in combination therapies with immune checkpoint inhibitors, CAR-T cells, and small molecule inhibitors, leading to more durable and potentially curative outcomes. Ongoing research and clinical trials are expanding their capabilities, paving the way for more effective, safer, and personalized treatments, positioning ADCs as a cornerstone of modern medicine and offering new hope to patients.

A Hydroxylamine-Mediated Amidination of Lysine Residues That Retains the Protein's Positive Charge

Lysine-specific peptide and protein modification strategies are widely used to study charge-related functions and applications. However, these strategies often result in the loss of the positive charge on lysine, significantly impacting the charge-related properties of proteins. Herein, we report a strategy to preserve the positive charge and selectively convert amines in lysine side chains to amidines using nitriles and hydroxylamine under aqueous conditions. Various unprotected peptides and proteins were successfully modified with a high conversion rate. Moreover, the reactive amidine moiety and derived modification site enable subsequent secondary modifications. Notably, positive charges were retained during the modification. Therefore, positive charge-related protein properties, such as liquid-liquid phase separation behaviour of α-synuclein, were not affected. This strategy was subsequently applied to a lysine rich protein to develop an amidine-containing coacervate DNA complex with outstanding mechanical properties. Overall, our innovative strategy provides a new avenue to explore the characteristics of positively charged proteins.

Noncanonical Amino Acids in Biocatalysis

In recent years, powerful genetic code reprogramming methods have emerged that allow new functional components to be embedded into proteins as noncanonical amino acid (ncAA) side chains. In this review, we will illustrate how the availability of an expanded set of amino acid building blocks has opened a wealth of new opportunities in enzymology and biocatalysis research. Genetic code reprogramming has provided new insights into enzyme mechanisms by allowing introduction of new spectroscopic probes and the targeted replacement of individual atoms or functional groups. NcAAs have also been used to develop engineered biocatalysts with improved activity, selectivity, and stability, as well as enzymes with artificial regulatory elements that are responsive to external stimuli. Perhaps most ambitiously, the combination of genetic code reprogramming and laboratory evolution has given rise to new classes of enzymes that use ncAAs as key catalytic elements. With the framework for developing ncAA-containing biocatalysts now firmly established, we are optimistic that genetic code reprogramming will become a progressively more powerful tool in the armory of enzyme designers and engineers in the coming years.

NSPs: chromogenic linkers for fast, selective, and irreversible cysteine modification

The addition of a sulfhydryl group to water-soluble N-alkyl(o-nitrostyryl)pyridinium ions (NSPs) followed by fast and irreversible cyclization and aromatization results in a stable S-C sp2-bond. The reaction sequence, termed Click & Lock, engages accessible cysteine residues under the formation of N-hydroxy indole pyridinium ions. The accompanying red shift of >70 nm to around 385 nm enables convenient monitoring of the labeling yield by UV-vis spectroscopy at extinction coefficients of ≥2 × 104 M-1 cm-1. The versatility of the linker is demonstrated in the stapling of peptides and the derivatization of proteins, including the modification of reduced trastuzumab with Val-Cit-PAB-MMAE. The high stability of the linker in human plasma, fast reaction rates (k app up to 4.4 M-1 s-1 at 20 °C), high selectivity for cysteine, favorable solubility of the electrophilic moiety and the bathochromic properties of the Click & Lock reaction provide an appealing alternative to existing methods for cysteine conjugation.

Organometallic Oxidative Addition Complexes for S-Arylation of Free Cysteines

Development of bioconjugation strategies to efficiently modify biomolecules is of key importance for fundamental and translational scientific studies. Cysteine S-arylation is an approach which is becoming more popular due to generally rapid kinetics and high chemoselectivity, as well as the strong covalently bonded S-aryl linkage created in these processes. Organometallic approaches to cysteine S-arylation have been explored that feature many advantages compared to their more traditional organic counterparts. In this Viewpoint, progress in the use of Au(III) and Pd(II) oxidative addition (OA) complexes for stoichiometric cysteine S-arylation is presented and discussed. A focus is placed on understanding the rapid kinetics of these reactions under mild conditions, as well as the ability to generate biomolecular heterostructures. Potential avenues for further exploration are addressed and usefulness of these methods to the practitioner are emphasized in the discussion.

Nanoparticles that Distinguish Chemical and Supramolecular Contexts of Lysine for Single-Site Functionalization of Protein

Lysine is one of the most abundant residues on the surface of proteins and its site-selective functionalization is extremely challenging. The existing methods of functionalization rely on differential reactivities of lysine on a protein, making it impossible to label less reactive lysines selectively. We here report polymeric nanoparticles that mimic enzymes involved in the posttranslational modifications of proteins that distinguish the chemical and supramolecular contexts of a lysine and deliver the labeling reagent precisely to its ε amino group. The nanoparticles are prepared through molecular imprinting of cross-linkable surfactant micelles, plus an in situ, on-micelle derivatization of the peptide template prior to the imprinting. The procedures encode the polymeric nanoparticles with all the supramolecular information needed for sequence identification and precise labeling, allowing single-site functionalization of a predetermined lysine on the target protein in a mixture.

Electrochemical Bioconjugation of Tryptophan Residues: A Strategy for Peptide Modification

Interest in electrocatalytic bioconjugation reactions has surged, particularly for modifying tryptophan and tyrosine residues in proteins. We used a cost-effective graphite felt electrode and low-current methodology to achieve selective bioconjugation of tryptophan with thiophenols, yielding up to 92%. This method exclusively labeled tryptophan residues and incorporated fluorinated tryptophan for NMR analysis. Eight polypeptides, including lanreotide and leuprorelin, were effectively coupled, demonstrating the method's versatility and potential for novel diagnostic and therapeutic agents.

Direct radical functionalization of native sugars

Naturally occurring (native) sugars and carbohydrates contain numerous hydroxyl groups of similar reactivity1,2. Chemists, therefore, rely typically on laborious, multi-step protecting-group strategies3 to convert these renewable feedstocks into reagents (glycosyl donors) to make glycans. The direct transformation of native sugars to complex saccharides remains a notable challenge. Here we describe a photoinduced approach to achieve site- and stereoselective chemical glycosylation from widely available native sugar building blocks, which through homolytic (one-electron) chemistry bypasses unnecessary hydroxyl group masking and manipulation. This process is reminiscent of nature in its regiocontrolled generation of a transient glycosyl donor, followed by radical-based cross-coupling with electrophiles on activation with light. Through selective anomeric functionalization of mono- and oligosaccharides, this protecting-group-free 'cap and glycosylate' approach offers straightforward access to a wide array of metabolically robust glycosyl compounds. Owing to its biocompatibility, the method was extended to the direct post-translational glycosylation of proteins.

Amplifiable protein identification via residue-resolved barcoding and composition code counting

Ultrasensitive protein identification is of paramount importance in basic research and clinical diagnostics but remains extremely challenging. A key bottleneck in preventing single-molecule protein sequencing is that, unlike the revolutionary nucleic acid sequencing methods that rely on the polymerase chain reaction (PCR) to amplify DNA and RNA molecules, protein molecules cannot be directly amplified. Decoding the proteins via amplification of certain fingerprints rather than the intact protein sequence thus represents an appealing alternative choice to address this formidable challenge. Herein, we report a proof-of-concept method that relies on residue-resolved DNA barcoding and composition code counting for amplifiable protein fingerprinting (AmproCode). In AmproCode, selective types of residues on peptides or proteins are chemically labeled with a DNA barcode, which can be amplified and quantified via quantitative PCR. The operation generates a relative ratio as the residue-resolved 'composition code' for each target protein that can be utilized as the fingerprint to determine its identity from the proteome database. We developed a database searching algorithm and applied it to assess the coverage of the whole proteome and secretome via computational simulations, proving the theoretical feasibility of AmproCode. We then designed the residue-specific DNA barcoding and amplification workflow, and identified different synthetic model peptides found in the secretome at as low as the fmol/L level for demonstration. These results build the foundation for an unprecedented amplifiable protein fingerprinting method. We believe that, in the future, AmproCode could ultimately realize single-molecule amplifiable identification of trace complex samples without further purification, and it may open a new avenue in the development of next-generation protein sequencing techniques.

Zirconium 89 and Copper 64 for ImmunoPET: From Antibody Bioconjugation and Radiolabeling to Molecular Imaging

Immunotherapy has transformed cancer treatment. Nevertheless, given the heterogeneity of clinical efficacy, the multiplicity of treatment options available and the possibility of serious adverse effects, selecting the most effective treatment has become the greatest challenge. Molecular imaging offers an attractive way for this purpose. ImmunoPET provides specific imaging with positron emission tomography (PET) using monoclonal antibodies (mAb) or its fragments as vector. By combining the high targeting specificity of mAb and the sensitivity of PET technique, immunoPET could noninvasively and dynamically reveal tumor antigens expression and provide theranostic tools of several types of malignancies. Because of their slow kinetics, mAbs require radioelements defined by a consistent half-life. Zirconium 89 (89Zr) and Copper 64 (64Cu) are radiometals with half-lives suitable for mAb labeling. Radiolabeling with a radiometal requires the prior use of a bifunctional chelate agent (BFCA) to functionalize mAb for radiometal chelation, in a second step. There are a number of BFCA available and much research is focused on antibody functionalization techniques or on developing the optimum chelating agent depending the selected radiometal. In this manuscript, we present a critical account of radiochemical techniques with radionuclides 89Zr and 64Cu and their applications in preclinical and clinical immuno-PET imaging.

Iron-Catalyzed C-H Alkylamination of Tyrosine Derivatives

An efficient method for the direct alkylamination of tyrosine derivatives via iron-catalyzed C-H amination has been developed. The method, using O-benzoyl-N,N-dialkylhydroxylamines as aminating agents, provides various C-amino-functionalized tyrosine derivatives in up to 77% yield. The utility of this method is showcased by its application to the direct introduction of drug molecules into tyrosine, facilitating access to structurally diverse amino-functionalized tyrosine derivatives.

Antibody-Drug Conjugates-Evolution and Perspectives

Antineoplastic therapy is one of the main research themes of this century. Modern approaches have been implemented to target and heighten the effect of cytostatic drugs on tumors and diminish their general/unspecific toxicity. In this context, antibody-drug conjugates (ADCs) represent a promising and successful strategy. The aim of this review was to assess different aspects regarding ADCs. They were presented from a chemical and a pharmacological perspective and aspects like structure, conjugation and development particularities alongside effects, clinical trials, safety issues and perspectives and challenges for future use of these drugs were discussed. Representative examples include but are not limited to the following main structural components of ADCs: monoclonal antibodies (trastuzumab, brentuximab), linkers (pH-sensitive, reduction-sensitive, peptide-based, phosphate-based, and others), and payloads (doxorubicin, emtansine, ravtansine, calicheamicin). Regarding pharmacotherapy success, the high effectiveness expectation associated with ADC treatment is supported by the large number of ongoing clinical trials. Major aspects such as development strategies are first discussed, advantages and disadvantages, safety and efficacy, offering a retrospective insight on the subject. The second part of the review is prospective, focusing on various plans to overcome the previously identified difficulties.

Cellular and Biophysical Applications of Genetic Code Expansion

Despite their diverse functions, proteins are inherently constructed from a limited set of building blocks. These compositional constraints pose significant challenges to protein research and its practical applications. Strategically manipulating the cellular protein synthesis system to incorporate novel building blocks has emerged as a critical approach for overcoming these constraints in protein research and application. In the past two decades, the field of genetic code expansion (GCE) has achieved significant advancements, enabling the integration of numerous novel functionalities into proteins across a variety of organisms. This technological evolution has paved the way for the extensive application of genetic code expansion across multiple domains, including protein imaging, the introduction of probes for protein research, analysis of protein-protein interactions, spatiotemporal control of protein function, exploration of proteome changes induced by external stimuli, and the synthesis of proteins endowed with novel functions. In this comprehensive Review, we aim to provide an overview of cellular and biophysical applications that have employed GCE technology over the past two decades.

Enzyme stability in polymer hydrogel-enzyme hybrid nanocarrier containing phosphorylcholine group

Enzymes are biological catalysts with good biocompatibility and high efficiency and have been widely used in many fields, such as wastewater treatment, biosensors, and the medical industry. However, their inherently low stability under conditions of practical use limits further applications. Zwitterionic polymers possessing a pair of oppositely charged groups in their repeating units can increase protein stability because of their good biocompatibility and high water content. In this study, zwitterionic copolymer nanogels comprising poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-methacrylic acid-N-hydroxy succinimide ester (MNHS)) (PMS) were synthesized via reversible addition-fragmentation chain-transfer polymerization (RAFT). β-Galactosidase (β-gal) was post-modified within zwitterionic polymer nanogels with a covalently-bound spacer and the activity was compared with that of directly immobilized β-gal and free β-gal. Compared with direct immobilization, covalent immobilization with a spacer could reduce the structural change of β-gal, as confirmed by the circular dichroism spectra. Although the activity of β-gal decreased after immobilization, the hybrids of the β-gal immobilized nanogels, termed hybrid nanogel-enzymes, demonstrated superior stability compared to the free enzymes. The hybrid nanogel-enzymes maintained their function against inactivation by organic solvents and proteinases owing to their high water content, anti-biofouling properties, and limited mass transfer. They can also withstand protein aggregation at high temperatures and maintain their activity. Compared to direct immobilization, immobilization with a spacer resulted in a dramatic increase in the enzyme activity and a slight decrease in the stability. These results indicate that polymer nanogels containing phosphorylcholine units are promising materials for enzyme immobilization, expanding the scope of enzyme applications.

Chemo- and regio-selective differential modification of native cysteines on an antibody via the use of dehydroalanine forming reagents

Protein modification has garnered increasing interest over the past few decades and has become an important tool in many aspects of chemical biology. In recent years, much effort has focused on site-selective modification strategies that generate more homogenous bioconjugates, and this is particularly so in the antibody modification space. Modifying native antibodies by targeting solvent-accessible cysteines liberated by interchain disulfide reduction is, perhaps, the predominant strategy for achieving more site-selectivity on an antibody scaffold. This is evidenced by numerous approved antibody therapeutics that have utilised cysteine-directed conjugation reagents and the plethora of methods/strategies focused on antibody cysteine modification. However, all of these methods have a common feature in that after the reduction of native solvent-accessible cystines, the liberated cysteines are all reacted in the same manner. Herein, we report the discovery and application of dehydroalanine forming reagents (including novel reagents) capable of regio- and chemo-selectively modifying these cysteines (differentially) on a clinically relevant antibody fragment and a full antibody. We discovered that these reagents could enable differential reactivity between light chain C-terminal cysteines, heavy chain hinge region cysteines (cysteines with an adjacent proline residue, Cys-Pro), and other heavy chain internal cysteines. This differential reactivity was also showcased on small molecules and on the peptide somatostatin. The application of these dehydroalanine forming reagents was exemplified in the preparation of a dually modified antibody fragment and full antibody. Additionally, we discovered that readily available amide coupling agents can be repurposed as dehydroalanine forming reagents, which could be of interest to the broader field of chemical biology.

Aromatic-Carbonyl Interactions as an Emerging Type of Non-Covalent Interactions

Aromatic-carbonyl (Ar···C═O) interactions, attractive interactions between the arene plane and the carbon atom of carbonyl, are in the infancy as one type of new supramolecular bonding forces. Here the study and functionalization of aromatic-carbonyl interactions in solution is reported. A combination of aromatic-carbonyl interactions and dynamic covalent chemistry provided a versatile avenue. The stabilizing role and mechanism of arene-aldehyde/imine interactions are elucidated through crystal structures, NMR studies, and computational evidence. The movement of imine exchange equilibria further allowed the quantification of the interplay between arene-aldehyde/imine interactions and dynamic imine chemistry, with solvent effects offering another handle and matching the electrostatic feature of the interactions. Moreover, arene-aldehyde/imine interactions enabled the reversal of kinetic and thermodynamic selectivity and sorting of dynamic covalent libraries. To show the functional utility diverse modulation of fluorescence signals is realized with arene-aldehyde/imine interactions. The results should find applications in many aspects, including molecular recognition, assemblies, catalysis, and intelligent materials.

Cysteine-Specific Multifaceted Bioconjugation of Peptides and Proteins Using 5-Substituted 1,2,3-Triazines

Peptide and protein postmodification have gained significant attention due to their extensive impact on biomolecule engineering and drug discovery, of which cysteine-specific modification strategies are prominent due to their inherent nucleophilicity and low abundance. Herein, the study introduces a novel approach utilizing multifunctional 5-substituted 1,2,3-triazine derivatives to achieve multifaceted bioconjugation targeting cysteine-containing peptides and proteins. On the one hand, this represents an inaugural instance of employing 1,2,3-triazine in biomolecular-specific modification within a physiological solution. On the other hand, as a powerful combination of precision modification and biorthogonality, this strategy allows for the one-pot dual-orthogonal functionalization of biomolecules utilizing the aldehyde group generated simultaneously. 1,2,3-Triazine derivatives with diverse functional groups allow conjugation to peptides or proteins, while bi-triazines enable peptide cyclization and dimerization. The examination of the stability of bi-triazines revealed their potential for reversible peptide modification. This work establishes a comprehensive platform for identifying cysteine-selective modifications, providing new avenues for peptide-based drug development, protein bioconjugation, and chemical biology research.

Preclustering Gelatin for Faster-Forming Injectable Hydrogels: A Strategy for Fabricating 3D Hydrogel Scaffolds with Improved Cell Dispersion

Gelatin-based injectable hydrogels capable of encapsulating cells are pivotal in tissue engineering because they can conform to any geometry and exhibit physical properties similar to those of living tissues. However, the slow gelation process observed in these cell-encapsulating hydrogels often causes an uneven dispersion of cells. This study proposes an approach for achieving fast gelation of unmodified gelatin under physiological conditions through gelatin preclustering. By using tetrafunctional succinimidyl-terminated poly(ethylene glycol) as a clustering agent, the gelation process is successfully expedited fivefold without requiring chemical modifications, effectively addressing the associated challenges of uneven cell distribution.

Homogeneous multi-payload antibody-drug conjugates

Many systemic cancer chemotherapies comprise a combination of drugs, yet all clinically used antibody-drug conjugates (ADCs) contain a single-drug payload. These combination regimens improve treatment outcomes by producing synergistic anticancer effects and slowing the development of drug-resistant cell populations. In an attempt to replicate these regimens and improve the efficacy of targeted therapy, the field of ADCs has moved towards developing techniques that allow for multiple unique payloads to be attached to a single antibody molecule with high homogeneity. However, the methods for generating such constructs-homogeneous multi-payload ADCs-are both numerous and complex owing to the plethora of reactive functional groups that make up the surface of an antibody. Here, by summarizing and comparing the methods of both single- and multi-payload ADC generation and their key preclinical and clinical results, we provide a timely overview of this relatively new area of research. The methods discussed range from branched linker installation to the incorporation of unnatural amino acids, with a generalized comparison tool of the most promising modification strategies also provided. Finally, the successes and challenges of this rapidly growing field are critically evaluated, and from this, future areas of research and development are proposed.

Thermally Triggered Triazolinedione-Tyrosine Bioconjugation with Improved Chemo- and Site-Selectivity

A bioconjugation strategy is reported that allows the derivatization of tyrosine side chains through triazolinedione-based "Y-clicking". Blocked triazolinedione reagents were developed that, in contrast to classical triazolinedione reagents, can be purified before use, can be stored for a long time, and allow functionalization with a wider range of cargoes and labels. These reagents are bench-stable at room temperature but steadily release highly reactive triazolinediones upon heating to 40 °C in buffered media at physiological pH, showing a sharp temperature response over the 0 to 40 °C range. This conceptually interesting strategy, which is complementary to existing photo- or electrochemical bioorthogonal bond-forming methods, not only avoids the classical synthesis and handling difficulties of these highly reactive click-like reagents but also markedly improves the selectivity profile of the tyrosine conjugation reaction itself. It avoids oxidative damage and "off-target" tryptophan labeling, and it even improves site-selectivity in discriminating between different tyrosine side chains on the same protein or different polypeptide chains. In this research article, we describe the stepwise development of these reagents, from their short and modular synthesis to small-molecule model bioconjugation studies and proof-of-principle bioorthogonal chemistry on peptides and proteins.

Non-symmetric stapling of native peptides

Stapling has emerged as a powerful technique in peptide chemistry. It enables precise control over peptide conformation leading to enhanced properties such as improved stability and enhanced binding affinity. Although symmetric stapling methods have been extensively explored, the field of non-symmetric stapling of native peptides has received less attention, largely as a result of the formidable challenges it poses - in particular the complexities involved in achieving the high chemo-selectivity and site-selectivity required to simultaneously modify distinct proteinogenic residues. Over the past 5 years, there have been significant breakthroughs in addressing these challenges. In this Review, we describe the latest strategies for non-symmetric stapling of native peptides, elucidating the protocols, reaction mechanisms and underlying design principles. We also discuss current challenges and opportunities this field offers for future applications, such as ligand discovery and peptide-based therapeutics.

Enantioselective organocatalytic strategies to access noncanonical α-amino acids

Organocatalytic asymmetric synthesis has evolved over the years and continues to attract the interest of many researchers worldwide. Enantiopure noncanonical amino acids (ncAAs) are valuable building blocks in organic synthesis, medicinal chemistry, and chemical biology. They are employed in the elaboration of peptides and proteins with enhanced activities and/or improved properties compared to their natural counterparts, as chiral catalysts, in chiral ligand design, and as chiral building blocks for asymmetric syntheses of complex molecules, including natural products. The linkage of ncAA synthesis and enantioselective organocatalysis, the subject of this perspective, tries to imitate the natural biosynthetic process. Herein, we present contemporary and earlier developments in the field of organocatalytic activation of simple feedstock materials, providing potential ncAAs with diverse side chains, unique three-dimensional structures, and a high degree of functionality. These asymmetric organocatalytic strategies, useful for forging a wide range of C-C, C-H, and C-N bonds and/or combinations thereof, vary from classical name reactions, such as Ugi, Strecker, and Mannich reactions, to the most advanced concepts such as deracemisation, transamination, and carbene N-H insertion. Concurrently, we present some interesting mechanistic studies/models, providing information on the chirality transfer process. Finally, this perspective highlights, through the diversity of the amino acids (AAs) not selected by nature for protein incorporation, the most generic modes of activation, induction, and reactivity commonly used, such as chiral enamine, hydrogen bonding, Brønsted acids/bases, and phase-transfer organocatalysis, reflecting their increasingly important role in organic and applied chemistry.

Design of a recombinant asparaginyl ligase for site-specific modification using efficient recognition and nucleophile motifs

Asparaginyl ligases have been extensively utilized as valuable tools for site-specific bioconjugation or surface-modification. However, the application is hindered by the laborious and poorly reproducible preparation processes, unstable activity and ambiguous substrate requirements. To address these limitations, this study employed a structure-based rational approach to obtain a high-yield and high-activity protein ligase called OaAEP1-C247A-aa55-351. It was observed that OaAEP1-C247A-aa55-351 exhibits appreciable catalytic activities across a wide pH range, and the addition of the Fe3+ metal ion effectively enhances the catalytic power. Importantly, this study provides insight into the recognition and nucleophile peptide profiles of OaAEP1-C247A-aa55-351. The ligase demonstrates a higher recognition ability for the "Asn-Ala-Leu" motif and an N-terminus "Arg-Leu" as nucleophiles, which significantly increases the reaction yield. Consequently, the catalytic activity of OaAEP1-C247A-aa55-351 with highly efficient recognition and nucleophile motif, "Asn-Ala-Leu" and "Arg-Leu" under the buffer containing Fe3+ is 70-fold and 2-fold higher than previously reported OaAEP1-C247A and the most efficient butelase-1, respectively. Thus, the designed OaAEP1-C247A-aa55-351, with its highly efficient recognition and alternative nucleophile options, holds promising potential for applications in protein engineering, chemo-enzymatic modification, and the development of drugs.

Solution-Phase Late-Stage Chemoselective Photocatalytic Removal of Sulfonyl and Phenacyl Groups in Peptides

Herein, BPC catalyzed visible-light-triggered target-specific late-stage solution phase desulfonylation from tryptophan in oligopeptides is portrayed by overcoming the isolation issue up to octamers. This robust and mild method is highly predictable and chemoselective, tolerating myriad of functional groups in aza-heteroaromatics and peptides. Interestingly, reductive desulfonylation is also amenable to biologically significant reactive histidine and tyrosine side chains, signifying the versatility of the strategy. Additional efficacy of BPC is demonstrated by solution phase phenacyl deprotection from C-terminal in peptides. Furthermore, excellent catalyst loading of 0.5 mol% and recyclability demonstrate the practical utility and applicability of this strategy.

Protein click chemistry and its potential for medical applications

A revolution in chemical biology occurred with the introduction of click chemistry. Click chemistry plays an important role in protein chemistry modifications, providing specific, sensitive, rapid, and easy-to-handle methods. Under physiological conditions, click chemistry often overlaps with bioorthogonal chemistry, defined as reactions that occur rapidly and selectively without interfering with biological processes. Click chemistry is used for the posttranslational modification of proteins based on covalent bond formations. With the contribution of click reactions, selective modification of proteins would be developed, representing an alternative to other technologies in preparing new proteins or enzymes for studying specific protein functions in different biological processes. Click-modified proteins have potential in diverse applications such as imaging, labeling, sensing, drug design, and enzyme technology. Due to the promising role of proteins in disease diagnosis and therapy, this review aims to highlight the growing applications of click strategies in protein chemistry over the last two decades, with a special emphasis on medicinal applications.

Recent Advances in Polymers Bearing Activated Esters for the Synthesis of Glycopolymers by Postpolymerization Modification

Glycopolymers are functional polymers with saccharide moieties on their side chains and are attractive candidates for biomaterials. Postpolymerization modification can be employed for the synthesis of glycopolymers. Activated esters are useful in various fields, including polymer chemistry and biochemistry, because of their high reactivity and ease of reaction. In particular, the formation of amide bonds caused by the reaction of activated esters with amino groups is of high synthetic chemical value owing to its high selectivity. It has been employed in the synthesis of various functional polymers, including glycopolymers. This paper reviews the recent advances in polymers bearing activated esters for the synthesis of glycopolymers by postpolymerization modification. The development of polymers bearing hydrophobic and hydrophilic activated esters is described. Although water-soluble activated esters are generally unstable and hydrolyzed in water, novel polymer backbones bearing water-soluble activated esters are stable and useful for postpolymerization modification for synthesizing glycopolymers in water. Dual postpolymerization modification can be employed to modify polymer side chains using two different molecules. Thiolactone and glycine propargyl esters on the polymer backbone are described as activated esters for dual postpolymerization modification.

An organometallic swap strategy for bottlebrush polymer-protein conjugate synthesis

Polymer-protein bioconjugation offers a powerful strategy to alter the physical properties of proteins, and various synthetic polymer compositions and architectures have been investigated for this purpose. Nevertheless, conjugation of molecular bottlebrush polymers (BPs) to proteins remains an unsolved challenge due to the large size of BPs and a general lack of methods to transform the chain ends of BPs into functional groups suitable for bioconjugation. Here, we present a strategy to address this challenge in the context of BPs prepared by "graft-through" ring-opening metathesis polymerization (ROMP), one of the most powerful methods for BP synthesis. Quenching ROMP of PEGylated norbornene macromonomers with an activated enyne terminator facilitates the transformation of the BP Ru alkylidene chain ends into Pd oxidative addition complexes (OACs) for facile bioconjugation. This strategy is shown to be effective for the synthesis of two BP-protein conjugates (albumin and ERG), setting the stage for a new class of BP-protein conjugates for future therapeutic and imaging applications.

Peptide recognition by a synthetic receptor at subnanomolar concentrations

This paper describes the discovery and characterization of a dipeptide sequence, Lys-Phe, that binds to the synthetic receptor cucurbit[8]uril (Q8) in neutral aqueous solution with subnanomolar affinity when located at the N-terminus. The thermodynamic and structural basis for the binding of Q8 to a series of four pentapeptides was characterized by isothermal titration calorimetry, NMR spectroscopy, and X-ray crystallography. Submicromolar binding affinity was observed for the peptides Phe-Lys-Gly-Gly-Tyr (FKGGY, 0.3 μM) and Tyr-Leu-Gly-Gly-Gly (YLGGG, 0.2 μM), whereas the corresponding sequence isomers Lys-Phe-Gly-Gly-Tyr (KFGGY, 0.3 nM) and Leu-Tyr-Gly-Gly-Gly (LYGGG, 1.2 nM) bound to Q8 with 1000-fold and 170-fold increases in affinity, respectively. To our knowledge, these are the highest affinities reported between a synthetic receptor and an unmodified peptide. The high-resolution crystal structures of the Q8·Tyr-Leu-Gly-Gly-Gly and Q8·Leu-Tyr-Gly-Gly-Gly complexes have enabled a detailed analysis of the structural determinants for molecular recognition. The high affinity, sequence-selectivity, minimal size of the target binding site, reversibility in the presence of a competitive guest, compatibility with aqueous media, and low toxicity of Q8 should aid in the development of applications involving low concentrations of target polypeptides.